1. Field of the Invention
This invention relates to an electric power tool in which a hydraulic pressure generator generates a plurality of impacts in one revolution thereof and a motor control method of the electric power tool.
2. Background Art
An electric power impact fastening tool as an electric power tool generally has a mechanism for generating one impact force per one revolution of a hydraulic pressure generator. (Refer to Patent Document 1.) In the electric power tool, a brushless DC motor is directly connected to an oil pulse unit to prevent occurrence of large vibration and reaction. (Refer to Patent Document 2.)
On the other hand, as an impulse wrench which is a hydraulic pressure power tool, there is a tool in which two impact forces per one revolution of a hydraulic pressure generator driven by compressed air (which will be hereinafter also called “two impacts per one revolution”). (Refer to Patent Document 3.) The tool of “two impacts per one revolution” generates a small torque and multiple impacts, thus a screwdriver, etc, is prevented from being away from a screw, etc. (which will be hereinafter called “come out”), at its operation time and an operation efficiency becomes good.
That is, a tool of “two impacts per one revolution” can perform a smooth fastening operation and a usability is good.
Patent Document 1: US2009/0133894
Patent Document 2: JP-A-2006-102826
Patent Document 3: JP-A-4-111779
A tool adopting the “two impacts per one revolution” as in Patent Document 3 is used for operations in which a rotation speed is small assuming a light load as compared with a tool of “one impact per one revolution”. The reason is that: if the tool of “two impacts per one revolution” and the tool of “one impact per one revolution” have the same impact mechanism in capability, one impact force of the tool of “two impact per one revolution” becomes half as compared with one impact force of the tool of “one impact per one revolution”, and an impact frequency of the tool of “two impact per one revolution” becomes twice of an impact frequency of the tool of “one impact per one revolution”. That is, in the tool of “two impact per one revolution”, an impact failure may occur because the impact frequency becomes high in a high load operation and responsibility of a hydraulic pressure generation mechanism worsens, etc. Here, the impact frequency means a frequency in impulse by oil compression of the hydraulic pressure generator.